Weather Briefing — La Rochelle → Gibraltar

Issued: Fri 17 Apr 2026 20:11 UTC · Advisory only — verify against local forecasts underway.

Current synoptic setup

The North Atlantic is dominated by a deep cut-off low near 58°N 40°W, central pressure ~985 hPa (Chart 2), with a cold 500 hPa core (-35 °C, 525 dam) — a classic spring Atlantic storm machine. A secondary low sits SE of Greenland (~995 hPa). A 1030 hPa high extends from the Azores toward Iberia, giving the route a weak ridge for now (Chart 1). Over the route itself, gradients are slack: Biscay shows 10–15 kt westerlies, Iberian coast 10 kt N'lies, Gulf of Cádiz light and variable (Chart 4). OPC 24 h (Chart 7) confirms only 1–2 m seas south of 45°N, with a 2 m NW swell working into the Portuguese coast. Satellite (Chart 8) shows the frontal cloud band draped W-to-E across the mid-Atlantic, still well west of the route.

72-hour outlook

Day 1 (Sat 18 Apr) — Biscay crossing.

WNW 12–18 kt, backing W. Seas 1.5–2 m in northern Biscay, dropping to 1–1.5 m south of 46°N (Chart 7). No frontal passage over the route — front remains ~15°W.

Day 2 (Sun 19 Apr) — Finisterre leg.

The Atlantic low deepens to ~985 hPa near 55°N 30°W (Chart 2) and its trailing front pushes east. Off Finisterre expect SW-W 18–25 kt, gusting 28 kt, with seas building to 2.5 m on the Iberian shelf (red arrow, Chart 6). Frontal passage possible late Sunday off NW Iberia — wind veer SW→NW, short squally period.

Day 3 (Mon 20 Apr) — Portugal to Cádiz.

A 1035 hPa high builds into Biscay/UK (Chart 3), while a deep 1010 hPa low parks west of Iberia at ~40°N 20°W. Squeeze between them drives N-NW 15–20 kt down the Portuguese coast (Portuguese trades setting up early), seas 1.5–2 m. Gulf of Cádiz / Gibraltar approach: NE 10–15 kt, levanter signature weak but watch the Strait.

Top 3 risks to watch

• Frontal passage off Finisterre Sunday night. Chart 2 shows the front reaching 15°W; timing uncertain ±6 h. Trigger to reroute: pressure falling faster than 2 hPa/3 h at sea → stand off or shelter Bayona/Leixões.
• New low west of Iberia at T+96 h (Chart 3). GFS shows a closed 1010 hPa low near 40°N 20°W with a cold 500 hPa pool (-30 °C). If it tracks east rather than stalling, Portuguese coast sees SW gale. Trigger: ECMWF agreement on eastward track in next run.
• Strait of Gibraltar wind funnel. Charts don't resolve it; synoptic gradient is light but local levanter/poniente accelerations are routine. Trigger: Tarifa observations >25 kt — time the transit for slack.

Routing considerations

Window is open — depart within 24 h. Crossing Biscay Saturday keeps you ahead of the Sunday front and ahead of the Day 3 Iberian low. Aim to be south of 43°N (Finisterre) by Sunday 12 UTC to stay in the southern/favourable semicircle of any trailing system — W-NW winds aft of the beam. Hug the Portuguese coast Monday to ride the building N'ly. Plan Strait transit on a west-going tide with confirmed <20 kt at Tarifa. Delaying departure beyond Sunday risks being caught by the T+96 h low on the Portuguese leg.